The present invention relates to an aqueous ink composition having high water resistance and excellent age stability and resistance to drying-up.
A variety of researches and developments with reference to aqueous ink compositions having water resistance have hitherto been conducted.
The so-called pigment type aqueous inks containing pigments as the main elements are well-known to the art. However, these pigment type aqueous inks are poor in dispersion stability and have the problem of sedimentation of pigment particles with time. When these inks are used in writing instruments, they tend to plug the ink passages of the instruments and thus inhibit the flow of smooth ink. In this type of ink the deposits of pigment particles along with the evaporation of water causes the so-called drying-up phenomenon at the writing tip of a pen. The result is a deposit of the pigment particles and plugging of the ink passages of the writing instrument.
Accordingly, the art has devised an aqueous ink composition having high water resistance, excellent age stability and resistance to drying-up.
Research on the so-called dye type aqueous ink composition containing dyes as main elements has been conducted in order to solve the problems known in the art. This has lead to an examination of the requisite conditions of ink such as the water resistance.
It has been found that in order to impart water resistance to the written matter produced by the ink, it is required for the written characters to bond to the paper tightly, and thus various materials were examined from the aspect of their adhesion to paper.